This invention is directed in general to reproduction apparatus, and more particularly to a mechanism for accurately locating an electronic light emitting print head assembly in a reproduction apparatus relative to an image receiving member.
In reproduction apparatus, such as electrostatographic reproduction apparatus for example, it is general practice ro provide an electrostatic image receiving member movable along a path relative to electrostatographic process stations. The electrostatic image receiving member may be a dielectric web guided for movement along the path by support rollers. In the electrostatographic process stations, a uniform electrostatic charge is applied to the dielectric member web and such charge is modified in an area of the web to form, in such area, a latent image charge pattern corresponding to information to be reproduced. The latent image charge pattern is then developed by applying pigmented marking particles to the web, and the developed image is then transferred to a final receiver member and fixed thereto by heat and/or pressure for example.
The mechanism by which modification of the uniform electrostatic charge pattern to form the latent image is accomplished is dependent upon the characteristics of the dielectric member. For example, if the dielectric member is of the type which merely retains charge on its surface, charge modification may be accomplished by selectively activating any of a plurality of electrodes to deposit or remove charge in selected areas of the member. If, on the other hand, the dielectric member is of the type having a photoconductive layer, charge modification is accomplished by exposing the member to light in an image-wise pattern.
Exposing of a dielectric member having a photoconductive layer has typically been accomplished by one of two methods. One method of exposure involves forming a light image of a document (generally referred to as optical copying). In this method, light is directed from a lamp assembly at a document with the light reflected from (or transmitted through) the document being directed through a lens unit into focus on the photoconductive surface. The light from the lamp may illuminate the entire document at one time (referred to as flash exposure), or may be passed through a slit and moved relative to the document to illuminate successive line segments of the document (referred to as scan exposure).
The second method of exposure involves the use of an electronically controlled light emitting print head assembly (generally referred to as nonimpact printing). Examples of electronically controlled light emitting print head assemblies include electro-optic gating devices, or arrays of light emitting diodes (LED's). The light emitting elements of an electronic print head assembly are selectively turned on and off to produce individual beams of light focused on the photoconductive layer of the image receiving member in order to expose the photoconductive layer in a line-by-line fashion. Information to be reproduced is electronically generated and is used to control the turning on and off of the light emitting print head assembly elements to form a desired charge pattern creating a latent image on the member corresponding in an imagewise configuration to the information to be reproduced.
The positioning of the print head assembly relative to the photoconductive layer of the image receiving member is of critical importance to assure that the light from the individual light emitting elements are in accurate focus on the photoconductive layer. U.S. Pat. No. 4,703,334 (issued Oct. 27, 1987, in the names of Mochimaru et al) shows a mechanism for positioning an electronically controlled light emitting print head assembly relative to an image receiving member. The mechanism of the Mochimaru et al patent requires structure to effect deflection of the image receiving member by a back-up roller associated with the print head assembly. This arrangement complicates the construction of the positioning mechanism and may adversely effect tracking of the image receiving member about its travel path. Further, it does not easily accommodate for necessary periodic changing of the image receiving member.